Merge r1774541 from trunk:

event: close a race condition where we might re-enable listeners while they
are already or about to be closed.


Submitted by: ylavic
Reviewed by: ylavic, jim, wrowe


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1783413 13f79535-47bb-0310-9956-ffa450edef68